Steam turbines receive an inlet flow of steam which is at very high temperatures and pressures. As a result, the portions of the steam turbine subjected to the high temperature flow of the steam are subjected to extreme operating conditions. To ensure reliability, it is often necessary to fabricate the elements of the steam turbine subjected to the high temperature flow from special materials that are capable of withstanding these extreme operating conditions.
Another approach is to provide cooling to those elements that are subjected to the high temperature flow so that the elements operate at lower temperatures. Providing such cooling can reduce the material requirements, which allows the elements to be made from lower cost materials.
As steam passes along the flow path through a steam turbine, it is gradually cooled. In some instances, steam turbines are designed to extract a portion of the steam passing along the flow path from a downstream location, and the extracted steam is routed to a location near the inlet to cool the elements located at the inlet. Lower temperature steam extracted from the downstream location can effectively cool the elements at the inlet that are subjected to the high temperature flow.